Derivative Financial Instruments - Summary of Proprietary Trading Activities (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Derivative [Line Items]
Proprietary Trading Activities Change In Fair Value	$ 1	$ 0	$ 0	$ 0
Proprietary Trading Activities Reclassification To Realized At Settlement	0	(1)	1	(2)
Proprietary Trading Activities Gain Loss Net	(11)	(40)	(18)	(35)
Operating Revenue [Member]
Derivative [Line Items]
Proprietary Trading Activities Change In Fair Value	(2)	0	(2)	1
Proprietary Trading Activities Reclassification To Realized At Settlement	(10)	(39)	(17)	(34)
Proprietary Trading Activities Gain Loss Net	(12)	(39)	(19)	(33)
Interest Rate Swap [Member] | Operating Revenue [Member]
Derivative [Line Items]
Proprietary Trading Activities Gain Loss Net	$ 1	$ (1)	$ 1	$ (2)